On the first 4 exams of her geometry class, Stephanie got an average score of 88. What does she need on the next exam to have an overall average of 90?
Answer: Let her score on the next exam be $x$ The sum of all of her scores is then $4 \cdot 88 + x$ The same sum must also be equal to $5 \cdot 90$ Solve: $x = 5 \cdot 90 - 4 \cdot 88 = 98$.